Continuous and asynchronous replication of a consistent dataset

ABSTRACT

Embodiments of the invention relate to creating and maintaining consistent data sets in a shared pool of configurable computer resources to support disaster recovery support. Data from an application is stored in local data storage and replicated to another data storage. A consistency point of the data is created in both of the data storage, with the consistency point representing an identical data set at a point-in-time. Based upon the created consistency points, a consistent set of application data may be requested to support a read operation for a migrated application.

BACKGROUND

This invention relates to application migration in a shared pool ofconfigurable computing resources. More specifically, the inventionrelates to creation of a consistent dataset in two storage subsystems tosupport the application migration.

Cloud computing is a model of service delivery for enabling convenient,on-demand network access to a shared pool of configurable computerresources, e.g. networks, network bandwidth, servers, processing,memory, storage, applications, virtual machines, and services, that canbe rapidly provisioned and released with minimal management effort orinteraction with a provider of service. One of the characteristics ofcloud computing infrastructure is that applications can be launched froma plurality of locations. Several factors drive the decision to launchan application in a specific data center, including resourceavailability, user location, disaster awareness, data location, andavailable facilities. However, the prior art cloud computingconfigurations do not provide flexible data migration with respect tothe application location.

BRIEF SUMMARY

This invention comprises a method, system, and article for creation ofconsistent data within an on-demand network accessible environment witha shared pool of configurable computing resources.

In one aspect, a method is provided for creation of consistent data in ashared pool of configurable resources. An application performs a writeoperation in which the application writes and stores write data in afirst data storage. As the application writes the data, in the firstdata storage file system data and metadata changes in the first datastorage are tracked. The tracked data and metadata changes areasynchronously synchronized to a second data storage. Thissynchronization provides a copy of the write data at a second location.To ensure consistency of the data at both the first and second datastorage, a first consistency point representing the file system data andmetadata is taken at a first point in time. In addition, a secondconsistency point is created in the second data storage, with the secondconsistency point representing the same file system data and metadata asthe first consistency point.

In a further aspect, a computer program product is delivered as aservice through a network connection. The computer program productcomprises a computer readable storage medium having computer readableprogram code embodied therewith. Computer readable program code isprovided for use with data storage to maintain and manage consistency ofdata within a shared pool of resources. More specifically, computerreadable program code is provided to support a write operation and tostore write data associated with the write operation in a first datastorage within the shared pool. Computer readable program code isprovided to track file system data and metadata changes in the firstdata storage with respect to the write data, and to asynchronously trackchanges to the data and metadata to a second data storage within thepool and in communication with the first data storage. In addition,computer readable program code is provided to create first and secondconsistency points associated with the write data. More specifically, afirst consistency point is created in the first data storage, with thefirst consistency point representing file system data and metadata at afirst point in time. The second consistency point is created in thesecond data storage, with the second consistency point representing thesame file system data and metadata as the first consistency point.

In a further aspect, a system is provided with a first data site havinga processor in communication with storage media. A functional unit isprovided in communication with the processor. The functional unitincludes tools to support creation and management of consistent data tosupport application migration. More specifically, the functional unitincludes a write manager, a track manager, a synchronization manager,and a consistency manager. The write manager addresses a write operationwherein an application writes data and stores the write data in thestorage media. The track manager, which is in communication with thewrite manager, tracks file system data and metadata changes in the firstdata site. The synchronization manager, which is in communication withthe track manager, asynchronously synchronizes the tracked data andmetadata changes to a second data site. Finally, the consistencymanager, which is in communication with the synchronization manager,supports synchronization of data in the first and second data sites.More specifically, the consistency manager creates a first consistencypoint in the first data site, with the first consistency pointrepresenting file system data and metadata at a first point in time. Theconsistency manager also creates a second consistency point in thesecond data site, with the second consistency point representing thesame file system data and metadata as the first consistency point.

In an even further aspect, a service is provided for creation ofconsistent data in a shared pool of configurable resources. Anapplication performs a write operation in which the application writesand stores write data in a first data site in the shared pool. As theapplication writes the data, file system data and metadata changes inthe first data site are tracked and the tracked changes areasynchronously synchronized to a second data site in the shared pool.This synchronization provides a copy of the write data at a secondlocation. To ensure consistency of the data at the first and second datasites, a first consistency point representing the file system data andmetadata is taken at a first point in time, including quiescing the filesystem and suspending processing of data and metadata in the first datasite. In addition, a second consistency point is created in the seconddata site, with the second consistency point representing the same filesystem data and metadata as the first consistency point. The process ofcreating the second consistency point also includes quiescing the secondfile system and suspending processing of data and metadata in the seconddata site.

Other features and advantages of this invention will become apparentfrom the following detailed description of the presently preferredembodiment of the invention, taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The drawings referenced herein form a part of the specification.Features shown in the drawings are meant as illustrative of only someembodiments of the invention, and not of all embodiments of theinvention unless otherwise explicitly indicated.

FIG. 1 depicts a cloud computing node according to an embodiment of thepresent invention.

FIG. 2 depicts a cloud computing environment according to an embodimentof the present invention.

FIG. 3 depicts abstraction model layers according to an embodiment ofthe present invention.

FIG. 4 depicts a flow chart illustrating steps employed for executing awrite operation to support creation of a backup copy at a remote datacenter in a shared pool of configurable computer resources.

FIG. 5 depicts a flow chart illustrating creation of consistency pointsin both the first and second file systems, with both consistency pointsrepresenting the same data.

FIG. 6 depicts a block diagram illustrating tools embedded in a computersystem to support both creation of a backup copy of data in a sharedpool of configurable resources, including creating consistency points intwo different file systems.

FIG. 7 depicts a block diagram showing a system for implementing anembodiment of the present invention.

DETAILED DESCRIPTION

It will be readily understood that the components of the presentinvention, as generally described and illustrated in the Figures herein,may be arranged and designed in a wide variety of differentconfigurations. Thus, the following detailed description of theembodiments of the apparatus, system, and method of the presentinvention, as presented in the Figures, is not intended to limit thescope of the invention, as claimed, but is merely representative ofselected embodiments of the invention.

The functional units described in this specification have been labeledas managers. A manager may be implemented in programmable hardwaredevices such as field programmable gate arrays, programmable arraylogic, programmable logic devices, or the like. The managers may also beimplemented in software for processing by various types of processors.An identified manager of executable code may, for instance, comprise oneor more physical or logical blocks of computer instructions which may,for instance, be organized as an object, procedure, function, or otherconstruct. Nevertheless, the executables of an identified manager neednot be physically located together, but may comprise disparateinstructions stored in different locations which, when joined logicallytogether, comprise the managers and achieve the stated purpose of themanagers.

Indeed, a manager of executable code could be a single instruction, ormany instructions, and may even be distributed over several differentcode segments, among different applications, and across several memorydevices. Similarly, operational data may be identified and illustratedherein within the manager, and may be embodied in any suitable form andorganized within any suitable type of data structure. The operationaldata may be collected as a single data set, or may be distributed overdifferent locations including over different storage devices, and mayexist, at least partially, as electronic signals on a system or network.

Reference throughout this specification to “a select embodiment,” “oneembodiment,” or “an embodiment” means that a particular feature,structure, or characteristic described in connection with the embodimentis included in at least one embodiment of the present invention. Thus,appearances of the phrases “a select embodiment,” “in one embodiment,”or “in an embodiment” in various places throughout this specificationare not necessarily referring to the same embodiment.

Furthermore, the described features, structures, or characteristics maybe combined in any suitable manner in one or more embodiments. In thefollowing description, numerous specific details are provided, such asexamples of an application manager, a replication manager, a migrationmanager, etc., to provide a thorough understanding of embodiments of theinvention. One skilled in the relevant art will recognize, however, thatthe invention can be practiced without one or more of the specificdetails, or with other methods, components, materials, etc. In otherinstances, well-known structures, materials, or operations are not shownor described in detail to avoid obscuring aspects of the invention.

The illustrated embodiments of the invention will be best understood byreference to the drawings, wherein like parts are designated by likenumerals throughout. The following description is intended only by wayof example, and simply illustrates certain selected embodiments ofdevices, systems, and processes that are consistent with the inventionas claimed herein.

A cloud computing environment is service oriented with a focus onstatelessness, low coupling, modularity, and semantic interoperability.At the heart of cloud computing is an infrastructure comprising anetwork of interconnected nodes. Referring now to FIG. 1, a schematic ofan example of a cloud computing node is shown. Cloud computing node (10)is only one example of a suitable cloud computing node and is notintended to suggest any limitation as to the scope of use orfunctionality of embodiments of the invention described herein.Regardless, cloud computing node (10) is capable of being implementedand/or performing any of the functionality set forth hereinabove. Incloud computing node (10) there is a computer system/server (12), whichis operational with numerous other general purpose or special purposecomputing system environments or configurations. Examples of well-knowncomputing systems, environments, and/or configurations that may besuitable for use with computer system/server (12) include, but are notlimited to, personal computer systems, server computer systems, thinclients, thick clients, hand-held or laptop devices, multiprocessorsystems, microprocessor-based systems, set top boxes, programmableconsumer electronics, network PCs, minicomputer systems, mainframecomputer systems, and distributed cloud computing environments thatinclude any of the above systems or devices, and the like.

Computer system/server (12) may be described in the general context ofcomputer system-executable instructions, such as program modules, beingexecuted by a computer system. Generally, program modules may includeroutines, programs, objects, components, logic, data structures, and soon that perform particular tasks or implement particular abstract datatypes. Computer system/server (12) may be practiced in distributed cloudcomputing environments where tasks are performed by remote processingdevices that are linked through a communications network. In adistributed cloud computing environment, program modules may be locatedin both local and remote computer system storage media including memorystorage devices.

As shown in FIG. 1, computer system/server (12) in cloud computing node(10) is shown in the form of a general-purpose computing device. Thecomponents of computer system/server (12) may include, but are notlimited to, one or more processors or processing units (16), a systemmemory (28), and a bus (18) that couples various system componentsincluding system memory (28) to processor (16). Bus (18) represents oneor more of any of several types of bus structures, including a memorybus or memory controller, a peripheral bus, an accelerated graphicsport, and a processor or local bus using any of a variety of busarchitectures. By way of example, and not limitation, such architecturesinclude Industry Standard Architecture (ISA) bus, Micro ChannelArchitecture (MCA) bus, Enhanced ISA (EISA) bus, Video ElectronicsStandards Association (VESA) local bus, and Peripheral ComponentInterconnects (PCI) bus. Computer system/server (12) typically includesa variety of computer system readable media. Such media may be anyavailable media that is accessible by computer system/server (12), andit includes both volatile and non-volatile media, removable andnon-removable media.

System memory (28) can include computer system readable media in theform of volatile memory, such as random access memory (RAM) (30) and/orcache memory (32). Computer system/server (12) may further include otherremovable/non-removable, volatile/non-volatile computer system storagemedia. By way of example only, storage system (34) can be provided forreading from and writing to a non-removable, non-volatile magnetic media(not shown and typically called a “hard drive”). Although not shown, amagnetic disk drive for reading from and writing to a removable,non-volatile magnetic disk (e.g., a “floppy disk”), and an optical diskdrive for reading from or writing to a removable, non-volatile opticaldisk such as a CD-ROM, DVD-ROM or other optical media can be provided.In such instances, each can be connected to bus (18) by one or more datamedia interfaces. As will be further depicted and described below,memory (28) may include at least one program product having a set (e.g.,at least one) of program modules that are configured to carry out thefunctions of embodiments of the invention.

Program/utility (40), having a set (at least one) of program modules(42), may be stored in memory (28) by way of example, and notlimitation, as well as an operating system, one or more applicationprograms, other program modules, and program data. Each of the operatingsystems, one or more application programs, other program modules, andprogram data or some combination thereof, may include an implementationof a networking environment. Program modules (42) generally carry outthe functions and/or methodologies of embodiments of the invention asdescribed herein.

Computer system/server (12) may also communicate with one or moreexternal devices (14), such as a keyboard, a pointing device, a display(24), etc.; one or more devices that enable a user to interact withcomputer system/server (12); and/or any devices (e.g., network card,modem, etc.) that enable computer system/server (12) to communicate withone or more other computing devices. Such communication can occur viaInput/Output (I/O) interfaces (22). Still yet, computer system/server(12) can communicate with one or more networks such as a local areanetwork (LAN), a general wide area network (WAN), and/or a publicnetwork (e.g., the Internet) via network adapter (20). As depicted,network adapter (20) communicates with the other components of computersystem/server (12) via bus (18). It should be understood that althoughnot shown, other hardware and/or software components could be used inconjunction with computer system/server (12). Examples, include, but arenot limited to: microcode, device drivers, redundant processing units,external disk drive arrays, RAID systems, tape drives, and data archivalstorage systems, etc.

Referring now to FIG. 2, illustrative cloud computing environment (50)is depicted. As shown, cloud computing environment (50) comprises one ormore cloud computing nodes (10) with which local computing devices usedby cloud consumers, such as, for example, personal digital assistant(PDA) or cellular telephone (54A), desktop computer (54B), laptopcomputer (54C), and/or automobile computer system (54N) may communicate.Nodes (10) may communicate with one another. They may be grouped (notshown) physically or virtually, in one or more networks, such asPrivate, Community, Public, or Hybrid clouds as described hereinabove,or a combination thereof. This allows cloud computing environment (50)to offer infrastructure, platforms and/or software as services for whicha cloud consumer does not need to maintain resources on a localcomputing device. It is understood that the types of computing devices(54A)-(54N) shown in FIG. 2 are intended to be illustrative only andthat computing nodes (10) and cloud computing environment (50) cancommunicate with any type of computerized device over any type ofnetwork and/or network addressable connection (e.g., using a webbrowser).

Referring now to FIG. 3, a set of functional abstraction layers providedby cloud computing environment (50) (FIG. 2) is shown. It should beunderstood in advance that the components, layers, and functions shownin FIG. 3 are intended to be illustrative only and embodiments of theinvention are not limited thereto. As depicted, the following layers andcorresponding functions are provided: hardware and software layer (60),virtualization layer (62), management layer (64), and workload layer(66). The hardware and software layer (60) includes hardware andsoftware components. Examples of hardware components include mainframes,in one example IBM® zSeries® systems; RISC (Reduced Instruction SetComputer) architecture based servers, in one example IBM pSeries®systems; IBM xSeries® systems; IBM BladeCenter® systems; storagedevices; networks and networking components. Examples of softwarecomponents include network application server software, in one exampleIBM WebSphere® application server software; and database software, inone example IBM DB2® database software. (IBM, zSeries, pSeries, xSeries,BladeCenter, WebSphere, and DB2 are trademarks of International BusinessMachines Corporation registered in many jurisdictions worldwide).

Virtualization layer (62) provides an abstraction layer from which thefollowing examples of virtual entities may be provided: virtual servers;virtual storage; virtual networks, including virtual private networks;virtual applications and operating systems; and virtual clients.

In one example, management layer (64) may provide the followingfunctions: resource provisioning, metering and pricing, user portal,service level management, and SLA planning and fulfillment. Thefunctions are described below. Resource provisioning provides dynamicprocurement of computing resources and other resources that are utilizedto perform tasks within the cloud computing environment. Metering andpricing provides cost tracking as resources are utilized within thecloud computing environment, and billing or invoicing for consumption ofthese resources. In one example, these resources may compriseapplication software licenses. Security provides identity verificationfor cloud consumers and tasks, as well as protection for data and otherresources. User portal provides access to the cloud computingenvironment for consumers and system administrators. Service levelmanagement provides cloud computing resource allocation and managementsuch that required service levels are met. Service Level Agreement (SLA)planning and fulfillment provides pre-arrangement for, and procurementof, cloud computing resources for which a future requirement isanticipated in accordance with an SLA.

Workloads layer (66) provides examples of functionality for which thecloud computing environment may be utilized. Examples of workloads andfunctions which may be provided from this layer includes, but is notlimited to: mapping and navigation; software development and lifecyclemanagement; virtual classroom education delivery; data analyticsprocessing; operation processing; and creation and maintenance ofconsistent application data to support migration within the cloudcomputing environment.

In the shared pool of configurable computer resources described herein,hereinafter referred to as a cloud computing environment, applicationsmay migrate to any data center, also referred to herein as a data site.There are two general scenarios in which an application is subject tomigration, including a planned migration and an unplanned migration. Ina planned migration, the application migrates to any data center in thecloud while maintaining disaster recovery support, and in an unplannedmigration, the application is subject to failure and recovers in anydata center in the cloud while maintaining disaster recovery support.Accordingly, the difference between a planned migration and an unplannedmigration is the failure and subsequent recovery of a failedapplication.

It is known that the current cloud computing models are not flexiblewith respect to disaster recovery. More specifically, it is known in theart that a failed application with associated supporting data mustrecover in a designated recovery center. The current models do notenable recovery at a location with consistent data in an efficientmanner. Accordingly, an efficient recovery based on consistent data atthe recovery center would enhance application recovery.

Regardless of the planned or unplanned form of migration, bothcategories of migration require a minimum amount of ‘critical’ data tobe transferred and cached to support application execution. All other‘non-critical’ data is asynchronously cached in the background so as notto interfere with running applications. FIG. 4 is a flow chart (400)illustrating steps employed for executing a write operation and storageof write data in the shared pool of configurable computer resources,hereinafter referred to as a cloud. Specifically, an application runs ata data center in the cloud (402). The application may support readand/or write operations. Data generated from a write operation is storedin data storage local to the data center in which the application isprocessing, e.g. local storage, also referred to herein as a first datastorage subsystem (404). For each write operation, it is determined ifthe write operation causes a change in either the data or metadata(406). A negative response to the determination at step (406) isfollowed by continued support of read and write operations at step(402). Conversely, a positive response to the determination at step(406) is following by employing a tool to track and record the changesto the data or metadata (408). More specifically, at step (408) datacreated from the write operation is tracked to identify changes in dataand/or metadata. Accordingly, for each write operation that result in adata or metadata change, such changes are tracked.

Different tools may be employed to address tracking of data and/ormetadata changes associated with a write operation. In one embodiment,an in-memory message queue is employed to track such changes. Morespecifically, a first in-memory message queue is associated with thefirst data storage subsystem, and a second in-memory message queue isassociated with a second data storage subsystem, which stores a replicaof data from the first storage subsystem. Following step (408) data ormetadata changes are sent to the in-memory message queue in the firststorage subsystem (410). To ensure that the change is reflected in thesecond data storage subsystem, the identified data or metadata change isasynchronously sent to the second in-memory message queue in the secondstorage subsystem (412). Accordingly, changes in data and/or metadatafrom a write operation are sent from the first storage subsystem to thesecond storage subsystem.

Replicating the tracked changes is one part in creating a second copy ofthe data at a second site. However, there is a latency associated withthe data replication. More specifically, in the event of failure of oneof the sites, i.e. the first or second data storage subsystem, the dataat both locations needs to be reconciled so that a backup applicationprocesses from the same data set at either location. To account for thelatency, consistency points of the data stored in both the first andsecond data storage subsystems are created to ensure that at a certainpoint in time the data in both file systems are equivalent. Accordingly,in the case of failure of either one of the file systems, the other filesystem may revert to the most recent consistency point and continueoperations.

FIG. 5 is a flow chart (500) illustrating the steps employed to supportcreation of consistency points in both the first and second file systemsassociated with the first and second sites, respectively, with bothconsistency points representing the same data. Before creation of afirst consistency point in the first data storage subsystem, the firststorage subsystem stops executing new messages in the queue (502). Alloutstanding messages in the queue that are in the process ofsynchronization to a data site must be completed before creation of aconsistency point. In one embodiment, items that are in the queue butnot in the process of synchronization may be associated with theconsistency point. Following step (502) it is determined if there aremessages in the queue that are in the synchronization process (504). Apositive response to the determination at step (504) is following bycompletion of the messages that are in the process of synchronization(506). Following either a negative response to the determination at step(504) or completion of the synchronization at step (506) the first filesystem is quiesced (508), which includes suspending processing of dataand metadata in the first queue, and a first consistency point iscreated in the first storage subsystem (510). Items that are in thequeue but not in the process of synchronization may be associated withthe first consistency point. The process of creating the consistencypoint at step (510) includes associating all changes of data andmetadata with the first storage subsystem. Once the first consistencypoint is created, the first file system is unquiesced (512). At the sametime, once the file system is unquiesced new messages can be received.Accordingly, the creation of the consistency point quiesces the filesystem and associates all data from the write operation(s) and data inthe queue with the created consistency point.

The creation of the first consistency point is local to the firststorage subsystem. However, in order to create a second consistencypoint local to the second storage subsystem that is equivalent to thefirst consistency point, the data from the write operation andassociated with the first consistency point must be flushed to thesecond storage subsystem. Following step (512), data from the in-memoryqueue that is associated with the first consistency point of the firstfile system is flushed to the second file system (514), where in oneembodiment the data is received in an in-memory queue local to thesecond storage subsystem. Once all data in the second queue that isassociated with the first consistency point is in the second storagesubsystem, a second consistency point is created in the second filesystem. More specifically, the process of creating the secondconsistency point includes quiescing the second file system (516) andcreating a second consistency point in the second storage subsystem(518). As noted above, quiescing the file system includes suspendingprocessing of data and metadata. Once the second consistency point iscreated, the second file system is unquiesced (520). Accordingly, theprocess of creating the second consistency point includes associatingall data and metadata of the first consistency point with the secondconsistency point so that the first and second consistency points andthe associated data are equivalent.

The process of creation of consistency points within the two separatefile system supports continuous data replication at the file level. Asshown in FIGS. 4 and 5, changes to data created in response to one ormore write operations are tracked and synchronized from the first datastorage system to the second data storage system. The continuousreplication of data across the storage system occurs in an asynchronousmanner. In addition, the continuous replication reduces the failurewindow between when a consistent data set is created in the first datastorage system and when it is fully replicated to the second datastorage system, thereby decreasing the amount of potential data loss inthe event of failure of the first storage system.

As shown in FIG. 5, the first consistency point of the first datastorage system may be created after data in the queue has been flushedinto the data storage subsystem. However, in one embodiment, thecreation of the first consistency point is undertaken on a periodicbasis, followed by creation of the second consistency point on thesecond storage subsystem. More specifically, a set of instructions mayestablish the frequency in which consistency points are created. Thefrequency ensures that on a periodic basis there will be a consistentset of data replicated across the first storage subsystems. In oneembodiment, the frequency is based upon creation of a consistency pointin the primary storage subsystem. For example, the consistency point iscreated on the first storage subsystem on the set frequency, while thesecond consistency point is created in the second storage subsystem whenreplication of data to support the equivalence of the first consistencypoint with the soon to be taken consistency point is complete. Becausethe second consistency point is created following completion of thereplication, a window between creation of the first and secondconsistency points is narrow. More specifically, the second consistencypoint is created following replication and is not subject to a setfrequency between creation of the first consistency point in the firststorage subsystem and creation of the second consistency point in thesecond storage subsystem. Accordingly, by establishing a set frequencyfor creation of consistency points in the first storage subsystem, awindow between the creation of the first consistency point and thecreation of the second consistency point is relatively narrow.

Migration of an application across storage subsystems may be planned orunplanned. Creation of the consistency points in the first and secondstorage subsystems ensures that should an application in one of thestorage subsystem be subject to a failure, the application can recoverfrom a consistent data set. By creation of two identical consistencypoints in two different storage subsystems, a failure associated withthe first consistency point enables recovery based upon the secondconsistency point. In one embodiment, the creation of the consistencypoint described herein is known as a snapshot, with the recovery from aconsistency point referred to as restoring a previous snapshot of thedata set. Accordingly, data and metadata from one or more writeoperations are stored in local data storage, i.e. a first storagesubsystem, and replicated to backup data storage, i.e. a second storagesubsystem, with creation of one or more consistency points in both datastorage locations.

As demonstrated in the flow charts of FIGS. 4 and 5, a method isemployed to support creation of first and second consistency points inboth first and second storage subsystems, respectively, with the firstand second consistency points referencing an identical data set. If anapplication referencing the data is subject to migration, either plannedor unplanned, disaster recovery is supported through the consistencypoints on two or more storage subsystems. In one embodiment, followingthe conclusion of either a planned migration or unplanned migration,application processing continues with data replication and creation ofconsistency points in at least two storage subsystems, i.e. data sites.FIG. 6 is a block diagram (600) illustrating tools embedded in acomputer system to support creation of identical consistency points inat least two storage subsystems. More specifically, a shared pool ofconfigurable computer resources is shown with a first data site (610)and a second data site (650). Although two data centers are shown in theexample herein, the invention should not be limited to the quantity ofdata site illustrated herein. In one embodiment, the first data sitesupports a first data storage system and the second data site supports asecond data storage system. Accordingly, two or more data sites may beemployed to support dynamic application migration.

Each of the data sites in the system is provided with at least oneserver in communication with data storage. More specifically, the firstdata site (610) is provided with a server (620) having a processing unit(622), in communication with memory (624) across a bus (626), and incommunication with first local storage (628), and the second data site(650) is provided with a server (660) having a processing unit (662), incommunication with memory (664) across a bus (666), and in communicationwith second local storage (668). The first and second data sites (610)and (650), respectively, communicate over a network (605).

In the example shown herein, a first functional unit (640) is providedlocal to the server (620) to process read and write operations local tothe first data site (610). Data from write operations are written to thefirst local storage (628), and replicated to the second local storage(668). In one embodiment, the replication to the second local storage(668) is limited to non-duplicate data.

Both the first and second data sites (610) and (650), respectively, eachhave tools to support and maintain creation of consistency points withinthe data local to the first and second data sites (610) and (650),respectively, such that the consistency points reference the same data.The first functional unit (640) is provided with several tools tosupport creation of the first consistency point in the first data center(610). The tools include, but are not limited to, a write manager (642),a track manager (644), a synchronization manager (646), and aconsistency manager (648). The write manager (642) is provided to writedata and to store the data in first local storage (628). It is known inthe art that a write operation may cause a change to a state of the datafrom before the write operation. As such, a track manager (644) isprovided in communication with the write manager. The track manager(644) is provided to track file system changes associated with the firstdata (610), including changes to both data and metadata resulting fromthe write operation. To maintain consistency of data between the datacenters, data from the first data center (610) is communicated to thesecond data center (650). A synchronization manager (646), incommunication with the track manager (644), is provided to synchronizethe tracked data and metadata changes from the first data center (610)to the second data center (650). In one embodiment, the synchronizationmanager (646) synchronizes the data between the data centers in either asynchronous or asynchronous manner. Accordingly, in response to a writeoperation that causes a change in data and/or metadata, changes aretracked and synchronized across the data centers.

To ensure that the data in both the first and second data sites areconsistent; a consistency manager (648) is provided in communicationwith the synchronization manager (646). The consistency manager (648) isresponsible for creation of one or more consistency points of theapplication data in the first local storage (628). To create aconsistency point in the first data site (610), the consistency manager(648) quiesces the local file system and suspends process of data andmetadata. In one embodiment, a message queue is provided to communicatedata and metadata changes across the data sites (610) and (650). Asshown herein, a first and second message queues (630) and (632),respectively, are both provided local to the first data site (610), anda third and fourth message queue (670) and (672), respectively, are bothprovided local to the second data site (650). Changes to data andmetadata by the write manager (642) are placed in message queue (630)and communicated to message queue (670) by the synchronization manager(646). With respect to creation of the consistency point in the filesystem, the consistency manager (648) suspends processing of data andmetadata in the first queue (630) prior to creation of the firstconsistency point, and associates all data and metadata chances in thefirst queue (630) with the first consistency point. In one embodiment,the consistency manager (648) flushes all of the messages in the firstqueue (630) to the third queue (670) prior to creation of the firstconsistency point.

As shown in FIG. 6, a second functional unit (680) is provided withseveral tools to support creation of a second consistency point in thesecond data site (650), with the second consistency point representingidentical file system data and metadata as the first consistency pointin the first data site (610). The tools include, but are not limited to,a write manager (682), a track manager (684), a synchronization manager(686), and a consistency manager (688), with these managers supportingparallel functionality as the managers in the first data site (610). Theconsistency manager (688) is responsible for creation of one or moreconsistency points of the application data in the second local storage(668). To create a consistency point in the second data site (650), theconsistency manager (688) quiesces the local file system and suspendsprocessing of data and metadata in the third queue (670) prior tocreation of the second consistency point, and associates all data andmetadata changes in the third queue (670) with the second consistencypoint. Accordingly, a parallel set of managers are provided in thesecond data site (650) to support creation of a second consistency pointin the second data site (650) that is identical to the first consistencypoint in the first data site (610).

Two message queues are shown in each of the data sites. Morespecifically, queues (630) and (632) are provided in the first data site(610) and queues (670) and (672) are provided in the second data site(650). As described herein, the first data site (610) represents aprimary data center with changes in data replicated to the second datasite (650) as a backup copy of the file system. Message queue (630) isemployed as a send queue, and message queue (670) is employed as areceive queue. In one embodiment, the second data site (650) mayfunction as a primary data center with a backup copy of the second filesystem retained local to the first data site (610). In this embodiment,message queue (672) is employed as a send queue, and message queue (632)is employed as a received queue. Accordingly, the second data site (650)may function as either a backup data site, or both a primary and abackup data site.

Consistent data replication is supported by the write, track,synchronization and consistency managers (642), (644), (646), and (648)of the first data site (610) and the write, track, synchronization andconsistency manager (682), (684), (686), and (688) of the second datasite (650). In one embodiment, the managers are provided in the sharedpool of configurable computer resources, i.e. cloud, to restore aprocessing element from a saved consistency point prior to execution ofthe processing element. The write, track, synchronization, andconsistency managers (642), (644), (646), and (648) of the first datasite (610) are shown residing in memory (624) of the server (620) localto the first data center (610), and the write, track, synchronization,and consistency managers (682), (684), (686), and (688) of the seconddata site (650) are shown residing in memory (664) of the server (660)local to the second data site (650). Although in one embodiment, themanagers may reside as hardware tools external to memory (624) and(664), respectively, they may also be implemented as a combination ofhardware and software. Similarly, in one embodiment, the managers may becombined into a single functional item that incorporates thefunctionality of the separate items. As shown herein, each of themanager(s) is shown local to one data site. However, in one embodimentthey may be collectively or individually distributed across a sharedpool of configurable computer resources and function as a unit to managecreation of identical consistency points in two different file systems.Accordingly, the managers may be implemented as software tools, hardwaretools, or a combination of software and hardware tools.

As will be appreciated by one skilled in the art, aspects of the presentinvention may be embodied as a system, method or computer programproduct. Accordingly, aspects of the present invention may take the formof an entirely hardware embodiment, an entirely software embodiment(including firmware, resident software, micro-code, etc.) or anembodiment combining software and hardware aspects that may allgenerally be referred to herein as a “circuit,” “module” or “system.”Furthermore, aspects of the present invention may take the form of acomputer program product embodied in one or more computer readablemedium(s) having computer readable program code embodied thereon.

Any combination of one or more computer readable medium(s) may beutilized. The computer readable medium may be a computer readable signalmedium or a computer readable storage medium. A computer readablestorage medium may be, for example, but not limited to, an electronic,magnetic, optical, electromagnetic, infrared, or semiconductor system,apparatus, or device, or any suitable combination of the foregoing. Morespecific examples (a non-exhaustive list) of the computer readablestorage medium would include the following: an electrical connectionhaving one or more wires, a portable computer diskette, a hard disk, arandom access memory (RAM), a read-only memory (ROM), an erasableprogrammable read-only memory (EPROM or Flash memory), an optical fiber,a portable compact disc read-only memory (CD-ROM), an optical storagedevice, a magnetic storage device, or any suitable combination of theforegoing. In the context of this document, a computer readable storagemedium may be any tangible medium that can contain, or store a programfor use by or in connection with an instruction execution system,apparatus, or device.

A computer readable signal medium may include a propagated data signalwith computer readable program code embodied therein, for example, inbaseband or as part of a carrier wave. Such a propagated signal may takeany of a variety of forms, including, but not limited to,electro-magnetic, optical, or any suitable combination thereof. Acomputer readable signal medium may be any computer readable medium thatis not a computer readable storage medium and that can communicate,propagate, or transport a program for use by or in connection with aninstruction execution system, apparatus, or device.

Program code embodied on a computer readable medium may be transmittedusing any appropriate medium, including but not limited to wireless,wireline, optical fiber cable, RF, etc., or any suitable combination ofthe foregoing.

Computer program code for carrying out operations for aspects of thepresent invention may be written in any combination of one or moreprogramming languages, including an object oriented programming languagesuch as Java, Smalltalk, C++ or the like and conventional proceduralprogramming languages, such as the “C” programming language or similarprogramming languages. The program code may execute entirely on theuser's computer, partly on the user's computer, as a stand-alonesoftware package, partly on the user's computer and partly on a remotecomputer or entirely on the remote computer or server. In the latterscenario, the remote computer may be connected to the user's computerthrough any type of network, including a local area network (LAN) or awide area network (WAN), or the connection may be made to an externalcomputer (for example, through the Internet using an Internet ServiceProvider).

Aspects of the present invention are described above with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems) and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer program instructions. These computer program instructions maybe provided to a processor of a general purpose computer, specialpurpose computer, or other programmable data processing apparatus toproduce a machine, such that the instructions, which execute via theprocessor of the computer or other programmable data processingapparatus, create means for implementing the functions/acts specified inthe flowchart and/or block diagram block or blocks.

These computer program instructions may also be stored in a computerreadable medium that can direct a computer, other programmable dataprocessing apparatus, or other devices to function in a particularmanner, such that the instructions stored in the computer readablemedium produce an article of manufacture including instructions whichimplement the function/act specified in the flowchart and/or blockdiagram block or blocks.

The computer program instructions may also be loaded onto a computer,other programmable data processing apparatus, or other devices to causea series of operational steps to be performed on the computer, otherprogrammable apparatus or other devices to produce a computerimplemented process such that the instructions which execute on thecomputer or other programmable apparatus provide processes forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

Referring now to FIG. 7 is a block diagram (700) showing a system forimplementing an embodiment of the present invention. The computer systemincludes one or more processors, such as a processor (702). Theprocessor (702) is connected to a communication infrastructure (704)(e.g., a communications bus, cross-over bar, or network). The computersystem can include a display interface (706) that forwards graphics,text, and other data from the communication infrastructure (704) (orfrom a frame buffer not shown) for display on a display unit (708). Thecomputer system also includes a main memory (710), preferably randomaccess memory (RAM), and may also include a secondary memory (712). Thesecondary memory (712) may include, for example, a hard disk drive (714)and/or a removable storage drive (716), representing, for example, afloppy disk drive, a magnetic tape drive, or an optical disk drive. Theremovable storage drive (716) reads from and/or writes to a removablestorage unit (718) in a manner well known to those having ordinary skillin the art. Removable storage unit (718) represents, for example, afloppy disk, a compact disc, a magnetic tape, or an optical disk, etc.,which is read by and written to by removable storage drive (716). Aswill be appreciated, the removable storage unit (718) includes acomputer readable medium having stored therein computer software and/ordata.

In alternative embodiments, the secondary memory (712) may include othersimilar means for allowing computer programs or other instructions to beloaded into the computer system. Such means may include, for example, aremovable storage unit (720) and an interface (722). Examples of suchmeans may include a program package and package interface (such as thatfound in video game devices), a removable memory chip (such as an EPROM,or PROM) and associated socket, and other removable storage units (720)and interfaces (722) which allow software and data to be transferredfrom the removable storage unit (720) to the computer system.

The computer system may also include a communications interface (724).Communications interface (724) allows software and data to betransferred between the computer system and external devices. Examplesof communications interface (724) may include a modem, a networkinterface (such as an Ethernet card), a communications port, or a PCMCIAslot and card, etc. Software and data transferred via communicationsinterface (724) are in the form of signals which may be, for example,electronic, electromagnetic, optical, or other signals capable of beingreceived by communications interface (724). These signals are providedto communications interface (724) via a communications path (i.e.,channel) (726). This communications path (726) carries signals and maybe implemented using wire or cable, fiber optics, a phone line, acellular phone link, a radio frequency (RF) link, and/or othercommunication channels.

In this document, the terms “computer program medium,” “computer usablemedium,” and “computer readable medium” are used to generally refer tomedia such as main memory (710) and secondary memory (712), removablestorage drive (716), and a hard disk installed in hard disk drive (714).

Computer programs (also called computer control logic) are stored inmain memory (710) and/or secondary memory (712). Computer programs mayalso be received via a communication interface (724). Such computerprograms, when run, enable the computer system to perform the featuresof the present invention as discussed herein. In particular, thecomputer programs, when run, enable the processor (702) to perform thefeatures of the computer system. Accordingly, such computer programsrepresent controllers of the computer system.

The flowcharts and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowcharts or block diagrams may represent a module, segment, or portionof code, which comprises one or more executable instructions forimplementing the specified logical function(s). It should also be notedthat, in some alternative implementations, the functions noted in theblock may occur out of the order noted in the figures. For example, twoblocks shown in succession may, in fact, be executed substantiallyconcurrently, or the blocks may sometimes be executed in the reverseorder, depending upon the functionality involved. It will also be notedthat each block of the block diagrams and/or flowchart illustration, andcombinations of blocks in the block diagrams and/or flowchartillustration, can be implemented by special purpose hardware-basedsystems that perform the specified functions or acts, or combinations ofspecial purpose hardware and computer instructions.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the present invention has been presented for purposes ofillustration and description, but is not intended to be exhaustive orlimited to the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the invention. Theembodiment was chosen and described in order to best explain theprinciples of the invention and the practical application, and to enableothers of ordinary skill in the art to understand the invention forvarious embodiments with various modifications as are suited to theparticular use contemplated.

Alternative Embodiment

It will be appreciated that, although specific embodiments of theinvention have been described herein for purposes of illustration,various modifications may be made without departing from the spirit andscope of the invention. In particular, the system can be configured tosupport creation of consistency point associated with a virtual machine.Accordingly, the scope of protection of this invention is limited onlyby the following claims and their equivalents.

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 8. A computer program product for use with adata storage subsystem, the computer program product comprising acomputer readable storage medium having computer readable program codeembodied thereon, which when executed causes a computer to implement themethod comprising: writing data and storing associated write data in afirst data storage local to a first data site; tracking file system dataand metadata changes in the first data storage; asynchronouslysynchronizing the tracked data and metadata changes to a second datastorage in communication with the first data storage; creating a firstconsistency point in the first data storage, the first consistency pointrepresenting file system data and metadata at a first point in time; andcreating a second consistency point in the second data storage, whereinthe second consistency point represents the same file system data andmetadata as the first consistency point.
 9. The computer program productof claim 8, further comprising employing one or more message queues tocommunicate data and metadata changes to the second data storage. 10.The computer program product of claim 9, wherein creating the firstconsistency point includes associating all outstanding data and metadatachanges in a message queue local to the first data storage with thefirst consistency point prior to creation of the second consistencypoint.
 11. The computer program product of claim 9, wherein creating thesecond consistency point includes all outstanding data and metadatachanges in the message queue local to the first data storage receivedand stored in the second data storage prior to creation of the secondconsistency point.
 12. The computer program product of claim 8, whereincreating the first consistency point includes quiescing a first filesystem in communication with the first data storage and suspendingprocessing of data and metadata in the message queue local to the firstdata storage prior to creation of the first consistency point.
 13. Thecomputer program product of claim 8, wherein the second data storage islocal to a second data site with a shared pool of resources separatefrom the first data site.
 14. A computer system comprising: a first datasite including a processor in communication with storage media; afunctional unit in communication with processor, the functional unitcomprising: a write manager to write data and store associated writedata in a first data storage local to a first data site; a track managerto track file system data and metadata changes in the first datastorage; a synchronization manager to asynchronously synchronize thetracked data and metadata changes to a second data storage incommunication with the first data storage; a consistency manager tosupport synchronization of data in the first data storage and the seconddata storage, the consistency manager to: create a first consistencypoint in the first data storage, the first consistency pointrepresenting file system data and metadata at a first point-in-time; anda second consistency point in the second data storage, wherein thesecond consistency point represents a same file system data and metadataas the first consistency point.
 15. The computer system of claim 14,further comprising one or more message queues to communicate data andmetadata changes to the second data storage.
 16. The computer system ofclaim 15, wherein the consistency manager associates all outstandingdata and metadata changes in a message queue local to the first datastorage with the first consistency point prior to creation of the secondconsistency point.
 17. The computer system of claim 15, wherein thesecond consistency point created by consistency manager includes alloutstanding data and metadata changes in the message queue local to thefirst data storage received and stored in the second data storage priorto creation of the second consistency point.
 18. The computer system ofclaim 14, wherein the consistency manager quiesces a first file systemin communication with the first data storage and suspends processing ofdata and metadata in a first message queue local to the first datastorage prior to creation of the first consistency point.
 19. Thecomputer system of claim 14, wherein the second data storage is incommunication with a second data site having a shared pool of resources,and the second data site is separate from a first data site incommunication with the first data storage.
 20. A service to supportmaintenance of consistent data sets comprising: writing data and storingassociated write data in a first data storage; tracking file system dataand metadata changes in the first data storage; asynchronouslysynchronizing the tracked data and metadata changes to a second datastorage in communication with the first data storage; creating a firstconsistency point in the first data storage, the first consistency pointrepresenting file system data and metadata at a first point in time; andcreating a second consistency in the second data storage, wherein thesecond consistency point represents the same file system data andmetadata as the first consistency point.
 21. The service of claim 20,further comprising employing a first message queue local to the firstdata storage to send data and metadata changes to the second datastorage, and a second message queue local to the second data storage toreceive the changes.
 22. The service of claim 21, wherein creating theconsistency point includes quiescing the file system, and suspendingprocessing of data and metadata in the message queue local to the datastorage prior to creation of the consistency point.
 23. The service ofclaim 21, further comprising further comprising scheduling creation ofthe first and second consistency points, including creating the firstconsistency point at the first data storage based upon a set frequency.24. The service of claim 23, further comprising creating the secondconsistency point at the second data storage following completion ofreplication of data from the first consistency point in the second datastorage.